4a. How is it that when you face a campfire at night, the front of your body can be uncomfortably hot while your back is cold?
- There are three different ways that heat can be emitted: convection, conduction, and radiation. In regard to the campfire, heat, through convection, rises upwards because the air is less dense. So really, the heat that you feel from the campfire is not due to convection. In this case, the air serves as the conductor. Because air is not the best at thermal conduction, there is a small chance that you would feel a lot of heat due to conduction. Radiation transmits heat through wavelengths of straight lines in an outward direction from the source; this would explain why only the front side of your body (the side facing the source of heat) feels hot, while your backside feels cool (https://science.howstuffworks.com/radiation.htm).
4b. You can reach into a 400oF conventional oven and pull out a sheet of hot aluminum foil with your bare hands without being injured. How can this be?
- While in the oven, the aluminum foil does get hot (as most things should). However, when you go to grab the aluminum foil, it doesn’t seem hot at the touch. This is because the foil has a very small mass and can only hold a small about of thermal energy. When you make contact with the foil with your hand (that has much more mass and heat capacity), the transfer of heat seems almost nonexistent (http://scienceline.ucsb.edu/getkey.php?key=703).
4c. Why does the interior of a car get extremely hot when parked in the sun on a hot sunny day? You need to appropriately mention convection, conduction and radiation in your answer.
- The thermal radiation from the sun is transmitted through glass and gets trapped inside the car due to the glass. Much radiation is entering the car, and little is leaving; hence why the car is hot (https://www.parkedinparadise.com/heat-transfer/). Conduction comes into play when the energy is transferred from the interior of the car to the air trapped inside the car. This is also where convection works because the less dense air moving upwards is being trapped, causing the already warm air to continue this process of heating up the car (https://news.wisc.edu/curiosities-does-a-dark-colored-car-heat-up-more-in-the-sun-than-a-light-colored-car/).
